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Патент USA US3100698

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Aug- 13, 1963
Filed June 17, 1960
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United States Patent ()1 "ice
Fatented Aug. 13, 1963
the high heat transfer advantage of a ?uidized bed to de
crease equipment size requirements together with means
George ll. Klein, Park Forest, Ralph E. Newby, Steger,
and Leo E. Post, (Ihicago, lit, assignors to Stautfer
Chemical €crnpauy, New York, N.Y., a corporation of
with means for recirculating ?uidizing gases, thus provid
ing a captive atmosphere which remains substantially dry
Filed June 17, 196%), Ser. No. 35,846
It (Ilairns. (Cl. 23-262)
The present invention is directed to an apparatus for
condensing or cooling phosphoric acid anhydride and its
which make the said ?uidized bed suitable for processing
hygroscopic materials which require the removal of heat.
This apparatus in its basic form contains ‘a ?uidized bed
in what may be called a closed circuit system.
In other
words the ‘apparatus provides an endless, recirculating dry
10 atmosphere.
The preferred embodiment includes means
for conditioning the recirculating ‘atmosphere without af
fecting its dry quality furnishing an apparatus capable of
continuous condensation of sublimed phosphoric acid
reaction products. More speci?cally, it is directed to an
apparatus with means for housing a ?uidized bed of fine
Truly continuous condensation of phosphoric acid an
ly divided particles ‘and means included therewith for cool 15
hydride on a large scale in any apparatus requires the re
ing and maintaining a substantially dry atmosphere in said
moval or prevention of crust formations. Several means
?uidized bed.
are present in the preferred apparatus of this invention
The invention is especially applicable to the condensa
for preventing crusts: means are included for removing
tion of phosphoric acid anhydride (P205) from a reaction
mixture ‘formed by the oxidation of elemental phosphorus 20 from the recirculating gases the very small particles which
would {otherwise deposit on the internal surfaces of the
in dry air. This mixture, the initial step in the commer
cial route to solid P205, is a hot gas having a temperature
apparatus, the dense ?uidized bed used scours the ex
posed surfaces in the processing zone ‘and maintains them
free of crusts, and the location and ?ow path of the gaseous
hygroscopic (used ‘often ‘as a dehydrating agent) and a 25 feed are designed to obviate much of the crusting prob—
sublirnable material, its condensation to the solid form
The present invention, while very advantageous in the
from the aforesaid reaction mixture is a dif?cult opera
condensation of gaseous P205, is obviously not limited
tion to perform e?iciently.
thereto, but may be successfully employed to process va
Heretofore the principal commercial apparatus for con
variety of related chemical substances Whenever similar
densing gaseous‘ P205 necessitated its passage through
problems are encountered. While the best embodiment
large atmospheric surface condensers ‘or “:b‘arns" where
of the invention now known to us has been selected for
particles of solid P205 would form in the cooled gas and
presentation in the accompanying drawing, it is to ‘be
grow to sufficient size to precipitate out as a ?nely divided
understood that it is illustrative ‘only, and not limiting,
material. A typical apparatus of the prior art is shown in
Chemical Engineering, vol. ‘61, September 1954, pp. 115 35 for obvious changes in ‘arrangement, construction ‘and de
tail can be made Without departing from the scope and
6. Because off-gases from the gaseous mixture were usu
ally discharged to the atmosphere from the surface con
spirit of the invention.
In the drawing, the apparatus contains a large vertical
densers, the condensing path was necessarily rather long
to insure essentially complete recovery of P205. Even 4-0 vessel or chamber for housing a bed of ?uidized particles.
Hereafter, this unit will be referred to ‘as. the “collector.”
with a very long condensing path this apparatus was in
Where used hereafter without further speci?cation, the
e?icient, ‘giving usually not more than ‘about 90% of the
of 300'—600° C. and containing appreciable quantities
of air ‘and residual nitrogen. Because P205 is extremely
term “bed” refers to a turbulent bed of ?uidized particles.
theoretically expected yield as ?nely divided P205, and
The remaining large units are ‘a combustion chamber, cy
somewhat noncontinuous, requiring frequent shut-down
for removal ‘of undesirable P205 crusts which invariably 45 clone separator, scrubber, ‘gas: cooler ‘and blower. For
greater clarity the description of the invention the units
formed about the heat transfer surfaces. These crusts
would act as \an insulation, decreasing the heat transfer
which require no new or involved designs features'to be ap
and minimizing the condensing capacity. Because the
apparatus was open to the atmosphere substantially dry
plicable to the invention are shown ‘only schematically.
ing continuous production, and di?iculties resulting in de
grading the product with moisture during condensation.
Liquid elemental phosphorus enters the combustion
chamber through line 1 and is oxidized by dry air enter
ing through line 2. The oxidation product is a gaseous
Where [a speci?c function ‘of ‘an element of the apparatus is
conditions were hard to maintain and product material 50 stated, such function may be explained in terms of its
applicability to the condensation of gaseous P205, but no
was susceptable to considerable degradation. However,
limitations should be implied therefrom since the prob
probably the most signi?cant disadvantage Was the great
lems encountered with P205 are generally those which
size and inherent expense of this ‘apparatus necessary for
hamper production of its derivatives and related comp
only a small product capacity.
pounds. The method ‘for condensing P205 in the present
In summary, the foremost problems encountered in
apparatus is more broadly explained in our copending U.S.
commercial production of P205, and ‘generally in the pro
duction of related compounds in which P205 is a reactant,
patent application Serial No. 21,499‘.
Our apparatus will now be more fully explained with
include excessive equipment size, loss of product contained
reference to the drawing which shows a preferred struc
in gases vented to the atmosphere, loss of product by its
formation as an undesirable crust, di?iculties in maintain 60 tural embodiment.
Because of the nature of these problems and the inability
of previous apparatus to cope with them, it is easily under
stood why our apparatus, described below, departs great
ly from that used heretofore in this ?eld.
mixture usually containing some excess air necessary to
insure complete combustion, the remaining nitrogen from
the reacted air, and P205 in the gaseous state. This mix
ture formed under moderately elevated pressure ?ows
from the combustion chamber through conduit 3 to the
densation of sublimed hygroscopic phosphoric acid an
collector. To prevent reverse ?ow in conduit 3, i.e.,
hydride in a substantially dry atmosphere. In addition,
the apparatus is suitable for cooling solid hygroscopic 70 carry-over of ?uidized solids from the collector back to
the combustion chamber when the latter is not in opera
P205, even after or during exothermic reaction with an
tion, several YObVlOllS modi?cations can be used. The
other substance. Our apparatus provides means for using
We have now devised an apparatus for continuous con
combustion chamber can be located above the level of the
?uidized bed 7 contained in the collector, or as shown in
the drawing, an inverted loop seal can beproduced with
conduit ‘3 rising above the bed level, dropping downward
thereafter to the point where it contacts the collector wall.
The fluidizing gas supplied to the windbox 13 ascends
through the constrictions in the horizontal gas distribut
ing partition 12 and rises through the bed 7. The gases
leaving the bed 7 pass upward through a supercontiguous
freeboard space 14 and then leave the collector through
conduit 15. The large particles suspended in these gases
The preferred feed line contains still another modi?ca
tion consisting of an extension 5 which is contiguous with
are separated in a cyclone and returned to the bed 7
conduit 3 projecting into the interior of the collector and
through dip leg 16. F'luostatic pressure forces ?nely di
providing a means for feeding the gas directly to the bed
vided product solids from the bed‘ through conduit 33
at a point away from the collector wall. The most ad 10 which contains a rotary paddle or star type valve 34.
vantageous results are achieved by pointing the extension
Static superatmospheric pressure is preferably used
5 downward with its opening in the bed positioned about
throughout the entire apparatus to eliminate leakage of
6 to about 18 inches above the horizontal partition 12‘.
air into the processing system through improper ?ttings
Extension 5 substantially minimized deposition of tacky
semi-solid crustations which would ordinarily (with a
conventional feed line terminating at the wall) constrict
or any of the conduits connected with the outside at
Thus moisture is prevented from entering
and degrading the hygroscopic product in a manner not
the opening and hamper or even suspend passage of gas
anticipated by the prior art equipment of this ?eld.
eous feed into the ?uidized bed. The recirculating sys
Very ?ne particles too small for separation by a cy
tem explained hereafter, in combination with the cooled
clone are removed in a wet separator employing a liquor
?uidized bed 7, has made it desirable to feed the gaseous 20 which ‘will not cause appreciable humidi?cation. This
P205 directly to the bed and not, as is usually the case
wet scrubber may consist as shown in the drawing of a
with somewhat analogous apparatus, indirectly through
the openings in the gas distributing partition 12. This
vertical unit with a packed bed 18 wherein the gases are
contacted with a suitable liquor. The scrubber liquor
need not be completely non-aqueous but should be of
uniobvious feed arrangement avoids a serious crusting
problem at the feed inlet and is considered a very de 25 suitable composition so that any contained water exerts
sirable feature of the invention.
only a small vapor pressure. To minimize vapor pres
The collector contains a horizontal gas distributing par
sure and also to help cool the recirculating gases this
tition 12 with subjacent lower compartment 13 which
liquor may be cooled before use in the scrubber. Since
serves as a windbox for the fluidizing gases, and a super
it is often desirable to augment the cooling capacity of the
jacent compartment for accorrrodating a ?uidized bed 7.
apparatus by external cooling of the ?uidizing gases this
The horizontal gas ‘distributing partition 12 contacts the
dual-purpose scrubbing operation can be advantageous.
collector walll around its periphery and contains a plural
When condensing gaseous P205 superphosphoric or poly
ity of openings for the constricted passage through the
phosphoric acid having a P205 content of about 77%
partition of a ?uidizing gas supplied under pressure to the
is a very suitable scrubber liquor capable of solubilizing
lower compartment 13. The openings in the horizontal
and removing essentially all the dispersed P205 from the
partition must provide even distribution of gases as they
recirculated gases.
rise into the ?uidized bed to allow for uniform ?uidiza
Dispersed particles of P205, if not removed, can be
tion of the particles and prevent quiescent zones where
very troublesome in an apparatus such as that of the
localized overheating may occur and disrupt e?'icient
present invention which employs recirculated gases. The
operation. The apparatus contains one or more vertical
recirculating gases are at a temperature usually much
cooling plates 8, of the type containing interior passages
below the condensation point of P205 and any ?ne dis
or voids for the circulation of a ?uid, located above the
persed P205 will ordinarily tend to deposit or condense
horizontal gas distributing grid 12. More precisely, these
on exposed surfaces. Particularly susceptable to this
plates are placed within the bed 7 but may extend slightly
phenomenon are the blower impeller, constrictions in the
into the space above. They serve as means for removing
gas distributing partition, and heat exchange surfaces out
heat. Although no speci?c arrangement of these plates 45 side of the ?uidized bed. These can be fouled to an ex
is necessary, where a large number are used some sym
tent requiring a costly and prolonged shut-down for the
metry is usually desirable. One advantageous arrange
purpose of cleaning out the apparatus. In view of these
ment, particularly for a large collector, is to place the
di?iculties, means for scrubbing the recirculated ?uidizing
plates radially, i.e., with their long horizontal axes falling 50 gas is a preferred, if not essential component of our ap
along lines projected ‘from the center of the bed to its
periphery. A cooling ?uid, usually Water or other liquid
The oif-gases leaving the cyclone through conduit 17
enters the vertical plates 8 through conduits 9 and after
enter the scrubber near the bottom thereof ascending
absorbing heat leaves through conduits 10. Both con
through a packed bed of Raschig rings 18 retained upon
duits 9 and 10V pass outside of the collector to their supply
a conventional support 19. The depth of this packed bed
and collecting means which are not of su?icient import
must be adequate to furnish thorough scrubbing ‘and will
to this invention to be shown in the drawing. These con
depend upon the variables involved (type of solvent,
duits can be secured to mounting ?anges 11 which are
bolted to the collector wall. Mounting ?anges ‘offer the
advantage of providing an air tight seal with an opening
at the wall through which the cooling plates and their as
sociated conduits may be conveniently removed from the
For its use as a condenser for a gaseous feed the bed
is composed of ?uidized solids having the same composi
temperature, throughput, etc.) in the particular opera
tion. At the top of the scrubber, immediately below the
gas exit, a mist screen 20‘ is positioned adjacent to the
walls ?lling the horizontal cross-section of the unit.
Scrubber liquor enters the unit through conduit 21 looat~
ed between the packing 1S and the mist screen 20, being
spnayed ‘downwiand on the bed through which it ?ows by
gravity. From the bottom of the packing the liquor drips
tion as the normally solid sublimed constituent in the 65 into the bottom of the 'scnubber vessel from where it is
gaseous feed. Thus, in the condensation of gaseous P205
from the phosphorus oxidation mixture mentioned pre
removed through conduit 22.
Regeneration equipment
may be used in connection with the scrubber liquor but
is not important to a description of the present invention
which act as nuclei for condensation.
and hence is not shown in the drawing. The path of the
A conventional feeder 6 for providing alternate means
recirculating gases in the scrubber shown in upward,
viously the bed is composed of ?uidized particles of P205
for ‘feeding the bed is shown only schematically. This
feeder may be used‘ during start up to initially charge the
collector with a bed of ?nely divided solids or, during
counterourrent to the descending liquor, leaving the unit
through conduit 23 connected at the top thereof.
A cooler for the recirculating gases is not a critical
continuous processing, for feeding ?nely divided solids. 75 part of the invention but as it can be advantageous in
many instances it is shown in the drawing. Principally,
the advantage of external cooling lies in its providing addi
ther combination of ‘features producing a device capable
of continuous condensation of a gaseous P205 mixture.
Continuous condensation requires the correct location of
feed, removal of very ?ne particles from the recirculat~
ing gas, bleed-off of the excess gases entering the system
with the feed, and other ‘features which will be obvious
to those familiar with the art.
tional capacity in the ?uidized bed. The cooler ?uidizing
gases returning to the bed absorb beat as they ascend
through the warmer mass augmenting cooling by the
vertical plates 8. When desirable to cool the recirculat
ing gases to ‘a rather low temperature the cooling alforded
by the use of a cool liquor in the scrubber may prove
Example 1
inadequate. 'In the drawing the recirculating stream is
shown passing into the gas cooler through conduit 23 10
The method shown in our copending application U.S.
and leaving through conduit 25 while the cooling ?uid
Serial No. 21,499, was applied to the condensation of
enters and leaves this unit through conduits 26‘ and 27,
phosphoric acid anhydride vapors, produced by the oxi
respectively. A desirable location for the cooler is after
dation of elemental phosphorus in dry air, in the apparatus
the scrubber Where the possibility of fouling its heat trans
of the accompanying drawing.
for surfaces is minimized.
This [apparatus consisted of all the components shown
A blower, preferably of the positive displacement type,
in FIGURE 1, except ‘for the entrainment screen and gas
supplies the necessary pressure rise in the recirculating
cooler and used superphosphoric acid (77% P205) as the
gases to overcome the resistances to gas flow throughout
scrubbing medium. The heat exchange apparatus con
‘the recirculating system and the collector. A line 28
sisted of two ?at plate coils positioned vertically in the
containing a normally closed valve and connected to con 20 bed section to face each other and partially divide the bed
‘duit’Z'S functions as an air inlet for start-up. Compressed
into compartments of about equal volume. A pre-estab
gases from the blower are delivered through conduit 29
lishedl bed of granular phosphoric acid ‘anhydride, made
to the lower compartment 13. Conduit means ‘for bleed
in the same apparatus by a previous run, was expanded to
ing-off excess gases from the recirculating stream are
a bed density of about 40‘ lbs/cu. ft. Fluidization was
shown connecting conduit 29 with the combustion cham 25 accomplished with recirculating gases passing up through
ber and the atmosphere. The valves 30‘ ‘and 31 are nor
the dense bed at a velocity of about 0.6 ft./sec. Phos
mally open while valve 32 is normally closed thereby
phoric acid anhyd-ride vapor containing 11-170 ppm.
‘forming a passage for gases to the outside atmosphere.
Water vapor was produced in the combustion chamber
However, under ‘alternate operating procedure bleed-off
and transported by conduit to the interior of the ?uidized
“gases can be recycled back to the combustion chamber. 30 bed near the bottom where it entered at a temperature of
This is accomplished with valves 30 and 32 open and
about 5-l0°—570° C. City water was circulated through
valve 31 either throttled or closed.
the cooling plates at a rate adjusted to produce a bed
The valved lines 4 and 24 connected to conduits 3 and
temperature of=129°i1° C. Under these conditions con
23, respectively, function as ‘feed lines for introducing
condensation was continued for many hours. A constant
gaseous reactants used in the preparation of P205 rea -
?ow of P205 vaporous ‘feed was maintained and con
tion products and for cleaning the apparatus. Gaseous
densed P205 ‘solids were withdrawn from the bed at about
ammonia may be introduced through lines 14 vand: 24 for
an equivalent rate.
reaction with gaseous or solid P205 to form certain am
walls and cooling surfaces in the ?uidization chamber
and the recirculating system were found to be perfectly
clean and free from crusts or scale. The over-all produc~
monia-phosphorus reaction products, the composition and
properties of which depend largely on the physical state
of the reacting P205. For example, gaseous ammonia in
.jected through line 4 into a gaseous P205 mixture yields
a feed which can be condensed in the collector to give a
At the termination of the run the
tion rate was vfound to be about 5 lbs./l1r./cu. ft. of
?uidized bed volume. The product was ‘a free-?owing,
virtually dustless form of hexagonal P205 in the shape
‘product substantially identical to Victamide, a complex
of small spheres or beads. The bulk density of this ma
ammonia-P205 reaction product described in US. Patent 45 terial was found to be about 67—74 lbs. per cu. ft.
2,122,122. Different products are made when gaseous
Example 2
ammonia is reacted with a bed of ?uidized P205 particles.
To prepare such products ammonia is injected into the
In an apparatus substantially as shown in the drawing
recirculating ?uidization gases through line 24.
a unique NET-P205 reaction product was prepared.
Condensation of a gaseous P205 mixture in the present 50 Gaseous ammonia ‘was reacted with precondensed spher
apparatus gives about 99+% of the theoretical stoichio
ical particles of P205 retained and ?uidized in the upper
metric yield as ?nely divide-d P205 solids. Virtually ‘all
compartment of the collector.
of this is in a usable desirable form free of large spurious
Initially the upper compartment of the collector was
particles or crusts of P205. Much of the very small loss
charged ‘with 600 lbs. of P205 produced by condensation
is due to solution of P205 in the scrubber liquor and there
as described in Example 1, above. This bed was ?uidized
fore is not truly a loss but a conversion of P205 to a dif
by starting the blower ‘and adjusting the gas rate. In
ferent useful form. Negligibly small losses are attribut
this run the Wet scrubber was eliminated, but in similar
able to the bleed-off gases or formation of P205 crusts.
runs it was used to remove both ?ne particles and am
Although a combustion chamber is shown in the draw
monia leaving the bed with the exhaust gases. After a
ing, it should be apparent that precondensed solids may 60 steady state was obtained with the P205 in a dense,
be sublimed to furnish feed through conduit 3 to the
turbulent ?uidized state and the recirculating gases sub
?uidized bed 7. This feed may be diluted with bleed-off
stantially ‘dry, gaseous ammonia was injected into the
gases obtained from conduit 29 through suitable transfer
recirculating gaseous atmosphere upstream of the blower.
lines or may be condensed in its pure undiluted form
65 A steady ?ow of ammonia gas was maintained until the
obviating bleed-off ‘from recirculating gases entirely. In
recirculating atmosphere contained about 5% by volume
fact it may be necessary, from a practical standpoint, to
admit small amounts of outside air into the recirculating
stream through valved line 255 when feeding a totally
of ammonia whereafter additional ammonia was added
as required to maintain this level. Contact between the
condensible stream.
ammonia-‘containing gases and the P205 particles in the
70 ?uidized bed resulted in an exothermic reaction. The
The gas recirculating and conditioning means already
bed temperature was held in the range of 100°~170° C.
by controlled circulation of cooling water through the
described is a principal feature of this invention since it
vertical plates. Entrai-ned particles were separated from
offers a way to maintain a substantially dry atmosphere
the dilute overhead phase and returned to the bed through
in combination with a ?uidized bed adapted to cooling
and/ or condensing. A preferred apparatus offers a fur 75 the dip leg. Samples of the reaction mass were period
ically taken from the bed through the discharge conduit
(B) Conduit means ‘for furnishing a gaseous feed of
P205 directly to the dense ?uidized bed and connect
and analyzed for nitrogen content. No additional feed
of P205 to the initial 600 lb. bed was allowed until the
ed through the wall of said vessel below the upper
analyzed material showed about 3% nitrogen by weight.
Thereafter, additional P205 was fed through the solids
level of said dense ?uidized bed and at a position
where said gaseous feed will enter said dense ?uidized
bed at least six inches above the horizontal gas dis
feed line to the upper ‘compartment. The gaseous am
monia feed was continued at its separate location while
tributing partition;
product solids containing ‘about 3—4% nitrogen were re
moved from the bed at a rate su?icient to give a constant
volume bed. The product of this run was a unique ma 1O
terial containing mainly P205 with a uniform, continuous
coating of a complex ammonia-P205 reaction product
about the outside of the individual P205 particles. This
(C) Val-ved conduit means for discharging condensed
particles of P205 under ?uostatic pressure from said
dense ?uidized bed and connected through the wall
of said vessel at a position within said upper com
partment ‘below the upper level of said dense ?uidized
coating serves to delay absorption of water by the very
hygroscopic P205 on the interior of the particle. Many 15
uses for materials of this nature are known. It may, for
example, be used where a delayed reaction is desirable
or where the P205 must be stored in a humid atmosphere
for a time, and where the ammonia contained in the par
(D) A recirculating and conditioning system for ex
hausted gases from said dense ?uidized bed com—
prising conduit means connected to said vessel near
the top and bottom thereof furnishing an endless
?ow path outside of said vessel in which a su?icient
quantity of said exhausted gases to support ?uidiz-a
tion may be recycled from said dense ?uidized bed
to said windbox, and dust separating means com
prising a wet scrubber for separating suspended par
ticles of P205 contained in said exhausted gases posi
tioned within said endless flow path;
(E) Heat transfer means for removing heat from said
dense ?uidized bed of P205 particles to maintain the
ticles is non~injurious or helpful in the ultimate use. One
speci?c example of where ammonia and P205 1are often
combined is in various fertilizer applications.
After the run the entire bed was discharged from the
collector and the interior of the unit was inspected. It
was found that ‘all surfaces, even those which crusted
slightly on previous condensation runs, were free of any
scale or crust.
required condensing temperature therein and posi~
The functions of several of the units shown can be
achieved with alternate types of equipment. For ex
ample, both mild, wet scrubbing ‘and gas compression can 30
tioned within said upper compartment with substan
tially all of the heat transfer surfaces below the up
be accomplished in ‘a single unit such as the Nash Hytor
per level of said dense ?uidized bed; and
(F) Valved conduit means for bleeding oif excess
Compressor. This unit is a centrifugal displacement com_
gases from said apparatus.
2. The apparatus of claim 1 wherein the gaseous feed
gas can be compressed [and at the same time cleaned by
conduit means project downward into the interior of the
contact with numerous droplets of the desired scrubber 35 ?uidized bed ‘and terminate within an opening substan
liquor which ?lls the interior of the compressor and
tially removed from the vessel walls :and about six to
through which the ‘gas must travel. A wet type dust
eighteen inches above the horizontal gas distributing par
separator is also adaptable to the apparatus of this inven
tion ‘although it does not allow return of the collected
3. The ‘apparatus of claim 1 wherein supplementary
solids to the bed. ‘Heat transfer equipment in the col
heat transfer means are provided within the recirculat
lector and/ or recirculating system is subject to consider
ing and conditioning system for cooling the recycled
pressor with an elliptical casing wherein the recirculating
alble modi?cation, e.g., cooling coils may be positioned
in the ?uidized bed, windbox, or scrubber as an equivalent
means for removing heat.
In commercial practices the complete apparatus is very
4. The combination consisting of the apparatus of
45 claim 1 with a combustion chamber for oxidizing ele
mental phosphorus and linked to the apparatus through
desirably connected in series or parallel with one or more
the gaseous feed conduit means.
essentially duplicate devices so as to furnish separate col
lectors for condensing, reacting, and even cooling ma
terials in a dry atmosphere.
Many variations and modi?cations are within the scope
and spirit of this invention, and therefore, no unnecessary
limitations should be understood from the above speci?
We claim:
1. An apparatus for condensing gaseous phosphoric
acid anhydride which comprises in combination:
(A) A vessel divided into upper and lower compart
ments by a horizontal gas distributing partition, said
References Cited in the ?le of this patent
Baily ________________ __ Aug. 8, 1939
' 2,847,360
Henninger et al. ______ __ Aug. 12, 1958
Haney ______________ __ Nov. 10, 1959
Cross et al. __________ __ June 13, 19611
Great Britain ________ __ Apr. 27, 1955
upper compartment serving to house a dense ?uidized
bed of cooled P205 particles ‘and said lower com—
partment serving as the ?uidization windbox;
Sittig: Article in Chemical Engineering, May 1953,
pages 219-231, 23—1F. (Copy in Sci. Lib, U.S.P.O.)
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